The increasing demand for high-speed voice and data communications has led to an increased reliance on optical communications, especially optical fiber communications. The use of optical signals as a vehicle to carry channeled information at high speed is preferred in many instances to carrying channeled information at other electromagnetic wavelengths/frequencies in media such as microwave transmission lines, coaxial cable lines, and twisted copper pair transmission lines.
Advantages of optical media include higher channel capacities (bandwidth), greater immunity to electromagnetic interference, and lower propagation loss. In fact, it is common for high-speed optical systems to have signal rates in the range of approximately several megabits per second (Mbit/s) to approximately several tens of gigabits per second (Gbit/s), and greater. However, as the communication capacity is further increased to transmit greater amounts of information at greater rates over fiber, maintaining signal integrity can be exceedingly challenging.
One way to more efficiently use available resources in the quest for high-speed information transmission is known as multiplexing, in which a plurality of channels are transmitted along an optical waveguide (e.g. an optical fiber). One particular type of multiplexing is wavelength division multiplexing (WDM). In WDM, each high-speed information channel has a center wavelength and prescribed channel bandwidth. At the receiver end, the plurality of optical channels is then separated and may be further processed by electronics. (By convention, when the number of channels transmitted by such a multiplexing technique exceeds approximately four, the technique is referred to as dense WDM or DWDM).
While transmission of information via an optical medium has offered significant improvements in information transmission, increased demand for capacity may still adversely impact signal quality during transmission. For example, the number of channels that can be carried in a single optical fiber is limited by cross-talk, narrow operation bandwidth of optical amplifiers, and optical fiber non-linearities.
Current wavelength channel center wavelengths, channel bandwidths and spacing between interleaved channels corresponding wavelengths preferably conform to an International Telecommunication Union (ITU) channel grid. For example, one ITU channel grid has a channel spacing requirement of 100 GHz. In this case, the channel spacing is referenced in terms of a frequency spacing, which corresponds in this example to a channel center wavelength spacing of 0.8 nm. With 100 GHz channel spacing, channel “n” would have a center frequency 100 GHz less than channel “n+1” (or channel “n” would have a center wavelength 0.8 nm greater than the center wavelength of channel “n+1”).
As can be appreciated, the more information that is sent over a particular medium, the greater the number of channels that are needed. It follows, that due to bandwidth considerations, the larger the number of channels, and the closer the separation between channels become. Among other difficulties, the decrease in channel spacing makes separating the plurality of optical channels more challenging. For example, in order to preserve the integrity of the signal at the receiver end of the communication link, cross-talk in the form of received channel overlap must be minimized. As can be appreciated, meeting these performance requirements of ever-increasing demand is a technical and practical challenge.
The technical and practical challenges described above are further exacerbated by environmental factors. These environmental factors can adversely impact the performance of the devices. One deleterious environmental factor is the ambient temperature. For example, in the change in the ambient temperature can create temperature induced wavelength drift of the WDM. This wavelength drift can cause wavelength channel overlap. In the closely spaced channels of ITU grids discussed above, optical system performance may be adversely impacted.
Accordingly, there is often a need to compensate for temperature fluctuations in WDM systems. While it may be possible to control the ambient temperature surrounding the WDM device, this generally requires rather elaborate climate control devices, which can be relatively complex and expensive. Moreover, these devices do not ensure the particular elements of a WDM are immune to temperature fluctuations. As such, in addition to adding complexity and expense, known active temperature control schemes may be unreliable.
Accordingly, what is needed is an optical interleaver/deinterleaver that caters to immediate and future needs for high speed optical networks without the disadvantages associated with current components and approaches.